The Supreme Court issued a compromise ruling in its first interpretation of a key human rights law yesterday, upholding the right of foreigners to seek compensation in U.S. courts for abuses that take place abroad but urging federal judges to interpret that right narrowly to avoid judicial interference in foreign affairs.

By a vote of 6 to 3, the court confirmed that the 1789 Alien Tort Statute (ATS) authorizes civil suits in this country for violations of international legal principles that are as universally recognized today as were rules against piracy or assaulting diplomats at the time the ATS was passed.

"[T]he judicial power should be exercised on the understanding that the door is still ajar subject to vigilant doorkeeping, and thus open to a narrow class of international norms today," Justice David H. Souter wrote for the majority. He alluded to the prohibition against torture as an example of such a norm.

The precise impact of the court's opinion on the many ATS-based suits now pending remains to be hashed out in lower courts, but the ruling clearly rebuffed an effort by the Bush administration and the business community to eliminate them.

In the background of the case was the prospect -- heightened by recent controversy over the degree to which the Bush administration has countenanced harsh procedures in interrogations of suspected terrorists or insurgents -- that the United States or its allies in the war on terrorism might be sued under the ATS for violating international law.

For their part, U.S. corporations hoped to stop a wave of suits that seek damages for companies' alleged collaboration in human rights abuses by authoritarian governments in countries where they do business.

Yesterday, Souter echoed the arguments of the administration and the corporations in warning courts to be "particularly wary of impinging on the discretion of the Legislative and Executive branches in managing foreign affairs."

In a footnote, Souter suggested that courts "should give serious weight" to arguments by the U.S. and South African governments that a pending class-action suit against U.S. firms for alleged collaboration with South Africa's apartheid-era governments would upset that country's reconciliation process.

Yet he offered only one clear example of an invalid human rights claim, and it was the one that prompted yesterday's case: the allegation by a Mexican, Humberto Alvarez-Machain, that a former Mexican police officer hired by the Drug Enforcement Administration to abduct him and bring him to the United States for trial in the slaying of a DEA agent was guilty of violating international law against "arbitrary arrest." (Alvarez-Machain was acquitted of murder.)

In a separate part of Souter's opinion that all eight of the other justices backed, the court also held that Alvarez-Machain could not sue the federal government for false arrest under a different statute, the Federal Torts Claim Act.

By saying that law did not bar the U.S. government from hiring or otherwise working with foreign agents abroad to arrest criminal suspects, the court gave the Bush administration support it said it needed to wage its battles against terrorism and drug trafficking.

But the main event was the court's discussion of the Alien Tort Statute, which was adopted by the First Congress and signed into law by President George Washington.

The law, which says that "district courts shall have original jurisdiction of any civil action for an alien for a tort only, committed in violation of the law of nations or a treaty of the United States," was probably initially intended to deal with cases in which foreign diplomats were victimized on U.S. soil.

The law had seldom been used until a federal appeals court interpreted it in 1980 to permit a suit in the United States by relatives of a 17-year-old Paraguayan against the man who allegedly tortured him to death in that country.

Since then, it has been used in cases against such defendants as Radovan Karadzic, the Bosnian Serb leader allegedly responsible for mass killings of Muslim civilians, and Unocal Corp., the petroleum multinational that is fighting a lawsuit over its alleged collaboration with the use of forced labor by Burma's government on a natural gas pipeline.

The Supreme Court had stayed out of the battle over the law. As recently as 2001, the court turned down an appeal by Royal Dutch Petroleum Co. in a suit by the survivors of Ken Saro-Wiwa, the human rights activist executed by Nigeria's government in 1995.

But since Sept. 11, 2001, several federal appeals judges who opposed the post-1980 interpretation of the ATS have written dissenting or concurring opinions urging the justices to clarify the law.

Justice Antonin Scalia, joined by Chief Justice William H. Rehnquist and Justice Clarence Thomas, objected to the part of Souter's opinion that permitted some suits under the ATS.

Scalia protested that the majority -- Justices John Paul Stevens, Sandra Day O'Connor, Anthony M. Kennedy, Ruth Bader Ginsburg and Steven G. Breyer, in addition to Souter -- should have blocked ATS suits altogether, because Congress never passed a law specifically authorizing them.

"For over two decades now, unelected federal judges have been usurping this lawmaking power by converting what they regard as norms of international law into American law," Scalia wrote. "Today's opinion approves that process in principle, though urging the lower courts to be more restrained."

The court, Scalia added, "wags a finger at the lower courts for going too far, and then . . . invites them to try again."

The consolidated cases decided yesterday are Sosa v. Alvarez-Machain, No. 03-339, and U.S. v. Alvarez-Machain, No. 03-485.

Humberto Alvarez-Machain was acquitted of murder after being abducted and brought to the United States for trial in the slaying of a Drug Enforcement Administration agent.